The present invention relates to a member arranged to act between two parts of a vehicle which are movable in relation to each other, wherein the member extends between said parts and comprises a first portion connectable to the first part of the vehicle and a second portion connectable to the second part of the vehicle, wherein the first portion comprises an elongated rod having external threads and the second portion a nut provided rotatably on the rod so that the length of the member, during a rotary motion between the rod and the nut, is variable in an axial direction, wherein an electric rotor machine having a stator and a rotor is arranged to influence said rotary motion and wherein the rotor and the nut are so located in relation to each other that at least one radial plane with respect to the axial direction extends both through the rotor and the nut.
In order to obtain a good comfort for passengers in a trackbound vehicle, it is usually equipped with members arranged to damp the motions of a car body in relation to an underlying bogie frame. In modern trackbound vehicles, members are also used which are arranged to displace the car body laterally in relation to the underlying bogie frame during travel in curves and also to tilt the car body for the purpose of further increasing the travel comfort for the passengers. Usually, such members are hydraulic or pneumatic. A disadvantage with the hydraulic or pneumatic members is that they are subject to faults and that they require a great deal of maintenance.
From DE 296 21 247 01 it is known to arrange an electrically driven member in a trackbound vehicle in order to control the tilting of the car body during travel in curves. The member is attachable between the car body and an underlying bogie frame and comprises two in relation to each other in the longitudinal direction displaceable portions. The first portion comprises a nut and the second portion an elongated threaded rod, which during rotation co-operates with the nut so that the length of the member may be changed. The second portion comprises for the rotation of the rod, an electric rotor machine having a stator and a rotor rigidly connected to the rod. The alternative possibility that the electric rotor machine may drive the nut instead of the rod is also indicated in the document.
In order for an electric rotor machine to be able to displace a car body in relation to a bogie frame without deteriorating the dynamic properties of the trackbound vehicle, the parts rotating with the rotor may not have a too large momentum of inertia. Therefore, the mass of said rotating parts ought to be as small as possible. A disadvantage with the known construction is that the motions of the rotor are transferred to the rod, which has a relatively large mass. Furthermore, the transmission between the rotor and the rod occurs at a first position whereafter the rotary motion of the rod is transferred to the nut at a second position located at a distance from the first position. Such a transmission comprises a considerable amount of losses. Therefore, the known electric member described above will presumably not function well in order to displace a car body.
The object of the present invention is to provide an electric driven member of the initially mentioned kind which has a relatively small and compact construction and which may act between vehicle parts of a considerable weight in a reliable way. Thereby, such an electric member may replace conventional hydraulic and pneumatic members.
This object is achieved by said member initially mentioned, which is characterised in that the rotor and nut are rigidly connected and constitute an integrated part. Thereby, no separate coupling device between the rotor and the nut needs to be provided and the losses of this power transmission are thereby nearly non-existent. Furthermore, a very short power transmission path is obtained for the transmission of the rotary motion of the rotor, via the nut, to the rod and vice versa. An electric member according the above may therefore be manufactured as a compact construction with few parts. Therefore, the member may also because of its simplicity be manufactured with a low cost. Furthermore, such a member is substantially cheaper in operation than conventional hydraulic and pneumatic members since it requires less maintenance.
According to a preferred embodiment of the invention, the nut comprises internally carried balls arranged to run along the external threads of the rod during the rotary motion of the nut. With such balls it is achieved that the friction between the nut and the rod during the rotary motion is very low at the same time as the balls allow a certain inclination of the rod in relation to the nut without any appreciable increase of the friction therebetween.
According to another preferred embodiment of the invention, the stator is rigidly connected to the second portion. Thereby, the second portion may have an inner cavity suited to receive the electric rotor machine whose stator, which usually has an external cylindrical-shape, is rigidly attached in said cavity in a suitable way.
According to another preferred embodiment of the invention, the electric rotor machine is arranged to displace said vehicle parts in relation to each other via the member, when needed. The member may thereby be coupled to a control unit, which, for example, senses the lateral acceleration of the vehicle and the mutual position of the vehicle parts, the direction of motion and the velocity. Depending on said sensed values, the control unit may initiate a displacement of said vehicle parts to a desired position by means of a suitable supply of energy to the electric rotor machine. The electric rotor machine may also be arranged to damp the motions between the vehicle parts via the member, when needed. Such a member may thereby replace conventional damper members of the hydraulic or the pneumatic type. Such members may therewith work as displacement members or damper members on, most preferably, both as displacement members and damper members.
According to another preferred embodiment of the invention, the electric rotor machine comprises a permanently magnetised synchronous motor. In this case, the rotor is permanently magnetised and will thereby rotate exactly with the rotation speed of the rotating magnetic field. The rotation speed of the rotor is decided by the current frequency in the stator windings and the number of poles. By such an electric rotor machine, it is easy to give the member a necessary control and thereby such properties that it becomes suitable as displacement member and damper member. Other types of electric rotor machines than a permanently magnetised synchronous motor are also possible to use in order to obtain said displacement and/or damping.
According to another preferred embodiment of the invention, the vehicle is a trackbound vehicle. In trackbound vehicles, the supply of electric energy is usually not a problem and it is usually an advantage to be able to replace hydraulic or pneumatic members by electric ones. This is due to the fact that the electric driven members with auxiliary equipment require substantially less maintenance than the hydraulic or pneumatic ones. Furthermore, they require less space and have a substantially lower weight. Advantageously, said first and second parts of the vehicle are a car body and a bogie frame. In trackbound vehicles such a member may mostly be intended to influence the motions of the car body, in order to improve the travel comfort for the passengers. The member may thereby be arranged to displace the car body laterally in relation to the bogie frame during travel of the trackbound vehicle in curves. Such a member may also be arranged to tilt the car body in relation to the bogie frame during travel in curves. Furthermore, such a member may be arranged to damp substantially all motions of the car body occurring during the travel of the trackbound vehicle. Such damping motions of the car body may be performed both vertically and horizontally.